Multi-pass image forming apparatus and image forming method using the same for providing plural print modes with different numbers of passes depending on desired print speed and image quality

Abstract

Provided are a multi-pass image forming apparatus and an image forming method using the same. The multi-pass image forming apparatus includes a plurality of developers for forming a plurality of electrostatic latent images using toners having different polarities and colors in one development process and for forming a multi-color image in at least two development processes; an exposure unit for forming the plurality of the electrostatic latent images on a photosensitive medium; and an intermediate transferring unit for having a toner images transferred thereon from the photosensitive medium that overlap to form the multi-color image, wherein the toner image may overlap another toner image on the intermediate transferring unit.

1. A multi-pass image forming apparatus comprising:
 a photosensitive medium; 
 an exposure unit for forming a plurality of electrostatic latent images on the photosensitive medium; 
 a plurality of developers containing color toners of yellow, cyan, magenta and black, respectively and sequentially disposed to face the photosensitive medium for developing the plurality of electrostatic latent images using two toners having different polarities and colors in one development process and for forming a multi-color image in at least two development processes; and 
 an intermediate transferring unit for having toner images transferred thereon from the photosensitive medium that overlap to form the multi-color image; 
 wherein the exposure unit includes a plurality of sub-driving units for selectively being turned on/off to charge the photosensitive medium to potentials corresponding to an image region onto which toners having different polarities and colors are transferred and a non-image region on which the image is not formed; 
 wherein the plurality of the sub-driving units includes a first sub-driving unit and a second sub-driving unit, 
 wherein the first sub-driving unit is turned on to charge the photosensitive medium with a latent image potential V 1  by which the toner having a negative polarity can be transferred, and the second sub-driving unit is turned on to charge the photosensitive medium with a non-latent image potential V md  by which the image is not formed, and both the first sub-driving unit and the second sub-driving unit are turned off to maintain the photosensitive medium with a surface potential V 0  by which the toner having a positive polarity can be transferred. 
 
   
   
     2. The apparatus according to  claim 1 , wherein any two developers selected from the plurality of the developers are brought into contact with the photosensitive medium to develop the plurality of the electrostatic latent images. 
   
   
     3. The apparatus according to  claim 2 , wherein the two developers contain toners having different polarities and colors, respectively. 
   
   
     4. The apparatus according to  claim 1 , further comprising a charging unit for making the toner images having different polarities formed on the photosensitive medium have a same polarity. 
   
   
     5. The apparatus according to  claim 4 , wherein the charging unit unifies the toner images having the different polarities into toner images having a positive polarity. 
   
   
     6. A multi-pass image forming apparatus comprising:
 a plurality of developers for forming a plurality of electrostatic latent images using toners having different polarities and colors in one development process and for forming a multi-color image in at least two development processes; 
 an exposure unit for forming the plurality of the electrostatic latent images on a photosensitive medium; and 
 an intermediate transferring unit for having toner images transferred thereon from the photosensitive medium that overlap to form the multi-color image; 
 wherein the plurality of developers contain the toners of different polarities and colors of yellow, cyan, magenta, red, green, and blue, and are sequentially transferred to face the photosensitive medium. 
 
   
   
     7. A multi-pass image forming apparatus comprising:
 a plurality of developers grouped two by two for developing a plurality of electrostatic latent images using toners having different polarities and colors in one development process and for forming a multi-color image in at least two development processes by rotation; 
 an exposure unit for forming the plurality of the electrostatic latent images on a photosensitive medium; 
 an intermediate transferring unit for having toner images transferred thereon from the photosensitive medium that overlap to form the multi-color image; and 
 a rotatable location control unit; 
 wherein the plurality of developers are grouped two by two so that one group has the toners of different polarities and different colors selected from yellow, magenta, cyan, red, blue, and green; and 
 wherein the plurality of developers are mounted in the rotatable location control unit, and any two developers selected from the plurality of the developers face the photosensitive medium to develop the electrostatic latent images on the photosensitive medium by rotation of the location control unit. 
 
   
   
     8. The apparatus according to  claim 7 , wherein the plurality of the developers forming one group contain toners having different polarities and colors. 
   
   
     9. The apparatus according to  claim 7 , further comprising a charging unit for making the toner images having different polarities formed on the photosensitive medium have a same polarity. 
   
   
     10. The apparatus according to  claim 9 , wherein the charging unit unifies the toner images having the different polarities into toner images having a positive polarity. 
   
   
     11. A multi-pass image forming apparatus comprising:
 a plurality of developers grouped two by two for forming a plurality of electrostatic latent images using toners having different polarities and colors in one development process and for forming a multi-color image in at least two development processes by rotation; 
 an exposure unit for forming the plurality of the electrostatic latent images on a photosensitive medium; and 
 an intermediate transferring unit for having toner images transferred thereon from the photosensitive medium that overlap to form the multi-color image; 
 the exposure unit includes a plurality of sub-driving units for selectively being turned on/off to charge the photosensitive medium to potentials corresponding to an image region onto which toners having different polarities and colors are transferred and a non-image region on which the image is not formed; 
 wherein the plurality of the sub-driving units includes a first sub-driving unit and a second sub-driving unit; 
 wherein the first sub-driving unit is turned on to charge the photosensitive medium with a latent image V 1  by which the toner having a negative polarity can be transferred, and the second sub-driving unit is turned on to charge the photosensitive medium with a non-latent image potential V md  by which the image is not formed, and both the first sub-driving unit and the second sub-driving unit are turned off to maintain the photosensitive medium with a surface potential V0 by which the toner having a positive polarity can be transferred. 
 
   
   
     12. In a multi-pass image forming apparatus comprising a plurality of pass print modes with each of the plurality of pass print modes comprising a different number of passes, a method of forming a multi-pass image comprising the steps of:
 selecting a pass print mode from among the plurality of pass print modes for printing the multi-color image in consideration of the print speed and the image quality; 
 operating a plurality of developers facing a photosensitive medium so as to form a toner images on the photosensitive medium, according to the selected pass print mode; and 
 transferring the toner images onto an intermediate transfer unit that overlap to print a multi-color image; 
 wherein if the selected pass print mode is a three-pass print mode, a plurality of electrostatic latent images are developed using a plurality of toners having different polarities and colors in a first pass, the plurality of the electrostatic latent images are developed using the plurality of the toners having the same polarities and colors as those of the first pass, and the plurality of the electrostatic latent images are developed using the plurality of the toners having polarities and colors different from those of the first pass in order to form the multi-color image. 
 
   
   
     13. A multi-pass image forming apparatus comprising:
 a plurality of developers for forming a plurality of electrostatic latent images using toners having different polarities and colors in one development process and for forming a multi-color image in at least two development processes; 
 an exposure unit for forming the plurality of the electrostatic latent images on a photosensitive medium; and 
 an intermediate transferring unit for having toner images transferred thereon from the photosensitive medium that overlap to form the multi-color image; 
 wherein the exposure unit includes a plurality of sub-driving units for selectively being turned on/off to charge the photosensitive medium to potentials corresponding to an image region onto which toners having different polarities and colors are transferred and a non-image region on which the image is not formed, and 
 wherein the plurality of the sub-driving units includes a first sub-driving unit and a second sub-driving unit, and 
 wherein the first sub-driving unit is turned on to charge the photosensitive medium with a latent image potential V 1  by which the toner having a negative polarity can be transferred, and the second sub-driving unit is turned on to charge the photosensitive medium with a non-latent image potential V md  by which the image is not formed, and both the first sub-driving unit and the second sub-driving unit are turned off to maintain the photosensitive medium with a surface potential V 0  by which the toner having a positive polarity can be transferred. 
 
   
   
     14. A multi-pass image forming apparatus comprising:
 a plurality of developers containing color toners of yellow, cyan, magenta, red, green and blue, respectively and sequentially disposed to face the photosensitive medium for forming a plurality of electrostatic latent images using two toners having different polarities and colors in one development process and for forming a multi-color image in at least two development processes; 
 an exposure unit for forming the plurality of the electrostatic latent images on a photosensitive medium; and 
 an intermediate transferring unit for having toner images transferred thereon from the photosensitive medium that overlap to form the multi-color image.